Treatment of petroleum oils



Patented June 2, 1936 UNITED STATES PATENT OFFICE TREATMENT OF PETROLEUM OILS N0 Drawing. Application November 2, 1934. Serial No. 751,261

, 5 Claims.

This invention relates to the treatment of petroleum oils and it comprises refining methods wherein oil is extracted with a composite difierential solvent comprising ethylene dichloride and methanol (a nonsolvent for the oil) and the mixture is allowed to stratify into an oil layer and a solvent layer, the oil layer being separated from the solvent layer and freed of residual solvents to recover an improved refined oil; all as more fully hereinafter set forth and as claimed.

In our copending application Serial No. 751,256, we have disclosed advantageous processes for refining petroleum oils with ethylene dichloride. The present invention is a modfication of and improvement upon the methods there described.

By the present methods hereinafter more fully described, we obtain substantial and important improvements in the viscosity-index, viscositygravity constant, carbon residue and other properties of the oil.

The viscosity-gravity relationship of oils is a good criterion for judging an oil and is much used as a standard in determining the characteristics of oils. See Hill & Ferris, Industrial & Engineering Chemistry, vol. 17, page 1250 (1925) and Hill & Coats, ibid. vol. 20, page 641 (June 1928). Those authors explain the viscositygravity constant and its significance.

The viscosity index (Dean & Davis, Oil & Gas Journal, March 31, 1932, page 92) is also much used in characterizing the viscosity-temperature relations of an oil, a high index indicating a flat viscosity-temperature curve. The differential solvents under discussion have a general effect in lowering the viscosity-gravity constant and raising the viscosity index.

In addition to the improvement in the products obtained, the present processes have certain advantages over the refining of petroleum oils with ethylene dichloride alone. In the methods described in our above acknowledged application Serial No. 751,256, the oil is extracted with ethylene dichloride at a suitable temperature. The temperature should be sufiicient to effect a clean stratification into an oil layer and a solvent layer. The two layers are separated and the ethylene dichloride is removed from each by distillation. By distilling off the ethylene dichloride an improved refined paraffinic oil is obtained and also as a separate product there is obtained a useful naphthenic oil.

To obtain clean Stratification and effective extraction, temperatures of about F. below the miscibility temperature of the oil with the solvent mixture may be employed. Of course that temperature may be varied to advantage with particular oils. Extraction at lower temperatures is advantageous. In some instances, temperatures as much as 100 F. below the miscibility temperature may be effectively employed, yet the actual operating temperature remains above that necessary with the use of ethylene dichloride, alone, as the solvent for the same oil. The general rule is that the temperature employed in a particular case is sufiicient. to give clean stratification and the desired extraction under the given conditions of operation.

In order to make clear our invention, the procedure of determining the miscibility temperature of an oil with a solvent is described. Equal volumes of the oil and the solvent are mixed in a test tube at a temperature at which complete solution occurs and the temperature of the mixture is then lowered slowly until precipitation of oil, as indicated by cloudiness in the liquid, occurs. The temperature at this point is the critical solution temperature or miscibility temperature for the particular oil and solvent in question. For instance, ethylene dichloride with a commercial Mid-Continent bright stock shows a miscibility temperature of minus 3 C. (26.6 F.)

Ethylene dichloride is an efiicient differential solvent for the separation of parafiinic and naphthenic constituents of oils, but because of its relatively low miscibility temperature it is necessary to efiect the separation at temperatures well below 32 F.

We have discovered that by using a mixture of ethylene dichloride and methanol we can secure eificient extraction at somewhat higher temperatures than when ethylene dichloride alone is used. This is because the miscibility temperature of ethylene dichloride-methanol mixtures with a given oil is appreciably higher than the miscibility temperature of ethylene dichloride alone with the same oils. For instance with the commercial bright stock mentioned ante, and a :25 mixture of ethylene dichloride and methanol, the miscibility temperature is 58 C. (136 F.). Methanol is a non-solvent for the oil. By using it admixed with the ethylene dichloride, we obtain improved results.

With such a mixture, the extractive power and F trol. The basic procedure is substantially the same as before. A mixed solvent containing ethylene dichloride and methanol in approximately the proportions between 60:40 and 80:20 are advantageous. A 75:25 mixture is satisfactory with most heavy stocks as mentioned ante.

One advantage of the present process is that the ethylene dichloride-methanol mixture has a higher miscibility temperature with the oil than does ethylene dichloride alone, consequently less refrigeration is necessary to obtain the desired stratification. With ethylene dichloride-methanol mixtures in the ratio specified and with an overhead cylinder stock made from Oklahoma crude, having a viscosity at 210 F. of 130 seconds Saybolt, clean Stratification can be effected at temperatures between 0 and 32 F. Generally, temperatures of at least 50 F. below the miscibility temperature of the oil and composite solvent should be used to obtain clean stratification into an oil layer and a solvent layer.

The methanol and ethylene dichloride are miscible with each other over the range of temperatures employed in these processes and the mixture functions as a unitary composite solvent.

In practicing the present invention, simple procedures may be employed. A sufiicient quantity of the composite solvent, usually from one to two volumes of solvent to one volume or" oil are mixed with the oil, the mixture is cooled to between 0 and 32 F. and maintained at that temperature, until clean stratification is obtained; usually not more than one-half hour is required. Then the oil layer and solvent layer are separated usually by drawing ofi the solvent layer. The improved refined oil is recovered by distilling off the solvent from the oil layer. Likewise the solvent may be recovered by distillation of the solvent layer, a naphthenic oil being also recovered,

Two or more extractions can be employed and the total volume of solvent may amount to three or more times the volume of oil being extracted. Continuous countercurrent operation, in which the oil and the extracting solvent are pumped countercurrent to each other in the proper volume ratio and at the proper temperature, may be used. Suitable heat exchange between the hot liquids and vapors and the cold liquids may be used to conserve heat and refrigeration.

The oil may be either preliminarily or subsequently dewaxed in a suitable manner.

Our invention may be employed in many and various embodiments. One advantageous embodiment which is typical and illustrative is as follows:

Example One hundred parts of overhead cylinder stock from Oklahoma crude are mixed with 200 parts of a 75 25 ethylene dichloride methanol solvent at about 75 F. The mixture is cooled to 32 F. and maintained at that temperature until clean stratification is obtained; about one-half hour is generally sufiicient. The solvent layer is drawn off and sent to storage. The oil layer is extracted twice in the same manner with 100 parts each of the composite solvent. The solvent layer is again drawn oil and sent to storage. The oil layer is then distilled at temperatures between 200 F. and 406 F. to remove the residual solvents. Fiftythree and five tenths parts by weight of an improved refined oil are obtained. This refined oil has the following properties as compared with the original stock:

Original Refined oil Specific gravity 0. 927 0.900 Viscosity at 210 Saybol 130. 0 00.1 Viscosity index 74. 92. 0 Viscosity-gravity constant 0. 853 0.823

and methanol in the proportions between 60 i; and 80 20 may be used in lieu of the 75 25 composite solvent.

Other advantageous modifications of this invention are believed clear to those skilled in the art and the embodiment given ante is merely illustrative of the invention.

What we claim is:--

1. In refining petroleum oils the improved process of solvent extracting with ethylene dichloride which comprises solvent extracting the oil with a composite solvent comprising a major amount of ethylene dichloride and a minor amount of methanol, thereby obtaining an improved extraction at higher temperatures than are permissible with ethylene dichloride alone.

2. The process of claim 1 wherein the said' composite solvent comprises ethylene dichloride and methanol in the ratios between 60 z 40 and 80 20 and said extraction is efiected at temperatures between 0 and 32 F. and wherein the oil layer is separated from the solvent layer and is freed of residual solvents by distillation to recover an improved refined oil.

3. As an improvement in refining petroleum oils by means of ethylene dichloride, the steps which comprise admixing one volume of said oil with between 1 and 2 volumes of a composite solvent comprising ethylene dichloride and methanol in ratios between 60 40 and 80 20, cooling the mixture to between 0 and 32 F. to stratify it 0 into an oil layer and a solvent layer and separating the two layers so obtained to efiect an improved solvent extraction of the oil by means of ethylene dichloride at higher temperatures than are permissible with ethylene dichloride alone.

4. The process of claim 3 wherein the said petroleum oil is a overhead cylinder stock, the said composite solvent in a 75 25 ethylene dichloride-methanol solvent mixture, the said mixing is at a temperature of about 75 F. and said cooling is to a temperature of about 32 F. and wherein the separated oil layer is subsequently freed of residual solvents by distillation at temperatures between 200 and 400 F.

5. The process of claim 3 wherein the said cooling is to at least F. below the miscibility temperature of said mixture of oil and composite solvent.

ERIC B. HJERPE. WILLIAM A. GRUSE. 

